Method of locating the fault in the case of multiconductor cables damaged by short-circuiting



1 y 5, 1932- w. GRAF METHOD OF LOCATING THE FAULT IN, THE CASE OF MULTICONDUC'I'OR CABLES DAMAGED BY SHORT CIRCUITING Flled July 11 1928 Patented July 5, 1932.

UNITED STATES PATENT OFFIQE WILHELM GRAF, 0]?

METHOD OF LOCATING THE FAULT IN THE BERLIN, GERMANY CASE OF MULTICONDUCTOR CABLES DAM- AGED BY SHORT-CIRCU ITIN G Application filed July 11', 1928, Serial No.

This invention relates to a method of locating the fault in the case of multi-conductor cables damaged by short-circuiting.

When all the conductors of a cable have been damaged by short-circuiting, it is in the case of all hitherto known methods a difficult matter without fault-less auxiliary conductor to determine with sufficient exactitude the point of the fault. The various methods cmplayed provide, generally speaking, satisfactory results only under certain conditions, and are therefore only capable of use to a limited extent. These methods may be divided into roughly two groups,the one being based on resistance measurement and the other on measurement of the drop in voltage.

The methods employing resistance measurement include, for example, that of Blavier, in which the resistance of a double conductor is first measured with insulated andthen with short-circuitcd ends, the fault being calculated from the two values. The fault resistance enters into both measuring values, and should, therefore, not vary to any appreciable F extent during the measurement; and for reasons which do not require discussion at the moment the same should be neither too high nor too low.

In the case of the second group of methods the fault is located by the drop in voltage which a current, to be maintained at a constant value, causes in the faulty conductor and in a known resistance connected in series therewith. The fault resistance must, therefore, in this case also be of substantial constancy, while in addition the same should not be greatly excessive, in order that sufiicient strength of current is obtainable.

It is the object of the present invention to rovide an entirely new method not disclosmg the limitations referred to. This method may be termed a branch current method, and has for its basis the following: Referring to the drawing: Fig. 1 is a view of connections illustrative 291,948, and in Germany July 16, 1927.

of the basic tion.

Figs. 2 to 6 illustrate connections performed over double leads and employing for measurement two conductors adjacent the battery conductors to obtain as strong a measuring current as possible.

Fig. 7 shows connections for a measuring apparatus for carrying out the method described herein.

If a voltage is applied to a conductorwith shunt connectionand a second conductor is earthed at both ends, as illustrated in Fig. 1 of the drawing, the current flows over shunt in part direct to earth and in part the same ponetrates into the earthed conductor and branches principle of the present invenofi towardsboth sides in reversed relation to the resistances. If at both ends of this conductor, which in the following will be termed the measuring conductor, a measuring instrument is connected, it is possible from the branching of the current to calculate the resistance of the measuring conductor section and accordingly the location of the fault.

On this basis a whole number of measuring connections may be developed, which allow the fault to be located in simple and reliable manner. Various examples are furnished in the following:

It may in the first place be remarked that it is preferable to perform the connections over double leads, as illustrated in Figs. 26, since when measuring with a single lead and earth the result may be incorrect due to the resistance of the earth connection. It is also advisable to select for the battery circuit such conductors as are spaced as wide apart as possible in the cable, and to employ for the measurement two conductors which are adjacent the battery conductors, in order to obtain as strong a measuring current as possible.

In Fig. 2 the two measuring conductors 1a and 2b are connected at the ends with sensitive current meters M of equal ohmic resist- I it is i occurring at the point ance and egual sensitiveness. The current reversed manner to the resistances:

i w a: M i, a: M

from which results -,,,M(a-a)+-:..w

iie Naturally, it is also possible to employ two dissimilar measuring instruments, in which case the formula must be altered accordingly. a

The reading must be performed simultaneously from both instruments, as the current tends on occasion to fluctuation due to polarization. The simultaneous reading is achieved by communication via telephone over the battery conductors, or a third double conductor. If in the case of very strong shunt telephonic communication is impossible, communication may be obtained by buzzer and telephonic receiver, or by other signalling means, for example by switching'ofi the battery for short periods, this being made noticeable on both measuring instruments simultaneously by return movement on the part of the pointers. The average of a plurality of varying readings on both sides may be taken.

If the fault resistance is so high that insufiicient movement on the part of the pointers is obtainable with the voltage at disposal, ossible to adopt the following course: The attery. is allowed to act for a few minutes on the fault until the current has become more or less constant, battery then being reversed by means of a commutator. By the depolarization thereby of the fault, the current increases for a moment, to then again drop. This is made noticeable on the measurin instruments in the following manner:

pon the reversal of the polarization the pointer suddenly moves towards the opposite side, proceeding from zero, at first advances rapidly and then slowly remains for a moment stationary and then returns again. The returning points of both instruments, which may readily be read, provide in reliable manner the proportion of the current branching, as the increase and drop in current as indicated by bothinstruments occurs perfectly synchronously. In this manner it is easily possible to obtain thirty times the amount of the permanent stroke, in addition.

no signals being required for simultaneous pointer movements of the polarization of the reading. This reversing operation may be repeated as often as desired, whereby the amount of the maximum stroke usually increases.

Fig. 3 shows a somewhat modified connection. In this case as much resistance R- is additionally connected on that particular side on which the measuring instrument first indicates the largest stroke of the pointer until both instruments indicate the same stroke. In this case t in-R 2' This method is naturally only advisable in such cases in which a telephonic communication between both measuring points is possible; the same, however, has the advantage of supplyin an'exact result even in the case of greatly uctuatin current, as the setting to equal strokes is simple and reliable; the strokes do not require to be recorded, and comparison between the two pointers need merely be made and if the same do not agree the resistance R adjusted accordingly.

In the'case of small strokes it is possible after the completed rough adjustment of the pointers to apply the polarization reversal as described above, for the purpose of obtaining a larger stroke and accordingly greater exactitude in the measurement.

A further connection is shown in Fig. 4. The general arrangement is the same as in the case of Fig. 2, whereby the measuring instruments M, however, may be short-circuited by means of the keys T and T Upon the measurement this occurs alternately, the stroke of the instrument which is not shortcircuited being noted. The proportion of the the two instruments then provides the reversedproportion of the cable .section formed by the faulty point.

If current is placed in 2, left jfiwhen T is depressed,

If now it is assumed that the total current in the measuring conductors remains unvaried whichever key be depressedan assumption which in practice is always fulfilled by suflicient approximit'y in view of the fact that due to electrolytic processes the the other part, which may The following three connections are in-' tended for such cases in which only one instrument is at disposal, or in which no assistance is available for attention to the second instrument.

Since in the case of these connections only one of the two branch currents is picked up in the measuring loop, two consecutive meas-. urements are necessary, in which the current branching is varied in a manner enabling calculation to be made, so that the point of fault may be determined from the two readings of the one instrument. In this case the same condition applies as previously set forth, viz., that the total current in the measuring loop remains unvaried upon the switching operation.

According to Fig. 5, the measuring conduct'or is alternately opened and closed at the one end by means of the key T, while at the other end the movements of the pointer of the measuring instrument M are read off.

When in the connection according to Fig. 5 the key T is opened, a part of the battery current flows over shunt through the cable stretch m and the measuring instrument M. The deflection of the pointer thus caused is J. If the key T is closed, a branching of the current occurs. The one part, which may be referred to as 2', proceeds over an and M, and be referred to as 2' proceeds over the right-hand cable section and T, the result being:

" uring loop occurs when closing the key T.

J is therefore=i+i or i ='Jz'. If this value is included in the above equation, the result will be and therefore Fig. 6 shows a connection, which allows the alternately,

pure-copper resistance of the measuring conductors to be determined without the point of the fault and the amount of its resistance having any effect on the result. For this purpose the key T is depressed and released the strokes performed by M being noted. If these are taken as J and z', the resistance of the double conductor is as follows:

The above equation according to Fig. 6 is derived as follows, the following designations being employed:

Left-hand section of the measuring line a:.

Current in a: with closed key J.

Current in ww with closed key J Current in a: with open key 2'.

Current in wa: with open key 5 The following equations result:

Since for the reasons set forth in the explanation of Fig. 5 the total strength of current in the measuring lines upon opening and Two measurements may also be combined, this resulting in certain advantages. If, for example inthe formula for connection 2 =i.)+i2-w i a 'w is taken the value from the TIP-33 'lU-ZE in place of formula for connection 3, i. e., w=2w+R, the following is obtained:

i. e., an equation in which the resistance to of the entire double conductor is not contained. This is frequently valuable, as in the case of a a strong shunt 10 may only be inexactly determined by ordinary resistance measure ment, and also the calculation from the length of cable and the kilometric average values unreliable.

It is, however, possible to find a useful formula for w if the equations covering to certain extent,

' is capable of also Figs. 2 and 3 are subtracted. The following is then obtained:

This value for 'w is in the case of a strong shunt more exact than according to the formula covering Fig. 6, as the same is wholly independent of the fault resistance.

In similar manner it is possible from a measurement according to Fig. 2 and a second similar one, in which a resistance R is additionally connected on the one side, to obtain the following formulae:

In this case 5 and 2' are the strokes performed by the instruments upon the first measurement, and i and 2' the strokes upon the second measuremen The measurements in the case of all these combinations are independent of each other, so that the fault resistance may be variable.

It may also be added that in the case of It will be understood that I do not limit myself to the various examples and combinav tions described, but that various other forms may be devised without departing from the spirit of the invention.

What I claim as new and desire to secure by Letters Patent is:

The method of ascertaining the location of a fault in a multi-core cable having intercore faults, consisting in connecting two of the cores at both ends into a loop, supplying these cores through other cores of the cable with current across the point of leakage to impress a potential difierence upon said first cores, and determining the proportion of the currents flowing in the two loops.

In testimony whereof I have affixed my signature.

WILHELM GRAF.

all connections the measurements may also be conducted with any foreign current available (for example, in the case oi telephone cables with current from an exterior or foreign battery), or with the polarization current possib y resulting at the fault itself by reason of electrolysis.

Fig. 7 shows a possible connection system for a measuring apparatus for carrying out the method described.

The key T in conjunction with the small resistance w has the object of practically short-circuiting the instrument in the normal position, in order to safeguard the same against unforeseen excess currents.

The plug resistance It enables the measuring scope of the instrument to be increased for example to twice, three or four times the amount. This has the object, when disturbing currents are resent, of being able to increase the measuring current in order to decrease the disturbing level, so that the disturbing currents are less noticeable.

The commutatorU serves for ready reversal of the polarization-namely, with the battery change as described.

In order to be able to follow the polarization reversal on the measuring instrument, the scale is preferably furnished with the zero point towards the left end, so that the pointer moving a few degrees towards the left.

In single leadst operations may be performed with earth'substituted for the second lead.

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